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What Actually Causes OCD?

There is no one definitive known cause for Obsessive Compulsive Disorder (OCD). However there are a number of theories and factors which are thought to increase an individual’s chances of developing OCD. This guide will take you through these factors in detail so you can gain a greater understanding of what causes OCD.


Biological Factors

Brain Differences

On brain scans, some areas of the brain have been shown to be different in those with OCD when compared to those without OCD. Specifically it has been shown that there are errors in the way areas of the brain communicate with one another. Beyond OCD explains that the areas of the brain primarily affected include, “the orbitofrontal cortex, the anterior cingulate cortex (both in the front of the brain), the striatum (or caudate nucleus), and the thalamus (deeper parts of the brain).”

The orbital-frontal cortex (OFC) is the area of the brain which detects when there is an outside threat. When it picks up on this, it sends a signal to the thalamus. The thalamus is responsible for sending out signals to the right parts of the brain to maintain communication, and in the case of a threat would send a signal back to the OFC, creating a loop or a circuit.

Another area of the brain near the thalamus called the caudate nucleus is like a brake pedal on a car. When it sees these threat signals coming through, it suppresses the ones which may not be real threats or are not important. However if the caudate nucleus is damaged or not working properly (as is thought to be the case in someone with OCD), the thalamus can become overactive, creating excessive threat signals, causing rising anxiety and leading to OCD symptoms.

This article from Stanford Medicine explains that, “inappropriately increased activity in the head of the caudate nucleus inhibits globus pallidus fibers that ordinarily dampen thalamic activity.” Significantly, the article also explains that MRI scans have also shown that the caudate nucleus is smaller in patients with OCD, which supports this theory. Some studies on these brain scans have also shown differences in the blood flow in the brain of those with OCD.

One theory suggests that the area of the brain which controls our ‘fight or flight’ response is not well regulated in patients with OCD. This means that the bodies and minds of those with OCD are constantly stuck in a state of high alert. We are not designed to deal with a prolonged stress reaction, and so this can take its toll. Among other effects it can cause us to be more fearful, hyperalert, more anxious, jittery and on edge.

Some research has revealed that the grey matter in the brains of OCD patients is increased in some areas and decreased in others when compared to those without OCD. Grey matter is responsible for controlling many important processes including our memories, emotional regulation, self-control, and decision making. You can see how when grey matter is out of balance, these functions can be disrupted and potentially contribute to OCD.

Chemical Imbalances

Some research suggests that those with OCD have chemical imbalances in the brain. Neurotransmitters are like chemical messengers which help areas of the brain communicate with one another, to keep our brains and bodies functioning in harmony. Levels of the neurotransmitters serotonin, dopamine and glutamate are significantly lower or higher respectively in OCD patients.

The neurotransmitter serotonin is responsible for regulating many of our biological and psychological processes, including maintaining our sense of wellbeing, regulating our emotions, helping us form memories and helping us sleep. When serotonin is lacking it can lead to mental illnesses such as depression, anxiety and OCD.

Dopamine is responsible for our mental wellbeing and how we respond to situations emotionally, as well as playing an important part in controlling movement. Among other important functions, glutamate is responsible for learning and memory processes. When these neurotransmitters are overactive, it can make it difficult for us to regulate our emotions, respond appropriately to situations, deal with challenges, and make adaptive (meaning helpful and positive) decisions. As with serotonin, this imbalance can lead to anxiety, depression, OCD and other mental illnesses.

This study from Oxford University Press concluded that, “the neurotransmitter model of OCD involves dopaminergic and glutamatergic overactivity in frontostriatal pathways, along with diminished serotonergic and GABAergic neurotransmission in frontolimbic systems.” The study goes on to conclude that these chemical imbalances can explain OCD activity within the brain.

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Studies have shown that there is a high genetic component with OCD. The inheritability of OCD can be estimated as being between 45-65%. This means that if someone you are related to has OCD, you are far more likely to develop it. These chances become further increased if you have a very close relative with OCD. The National Institute of Mental Health states that, “Twin and family studies have shown that people with first-degree relatives (such as a parent, sibling, or child) who have OCD are at a higher risk for developing OCD themselves.”

Research suggests that a mutation of the human serotonin transporter gene (hSERT) gene can cause OCD and other psychiatric disorders. This 2019 article also explains that some research suggests, “having particular versions or alleles of genes controlling the manufacture of serotonin, brain-derived neurotrophic factor (a chemical that plays a large role in controlling development of the brain) and glutamate may reflect some sort of vulnerability to developing OCD.”


Trauma can be defined as, “a psychological, emotional response to an event or an experience that is deeply distressing or disturbing.” There are many types of events which can be traumatic to an individual, and since we’re all different, we might all experience the same event differently. Types of trauma can include sexual abuse, physical abuse, mental abuse, a natural disaster, being involved an accident, losing someone close to you, and so much more.

When trauma is experienced in childhood, it can have an even more severe effect on the individual. When children are in their formative years and trauma is present, it can lead to many negative effects in their adult life which can be difficult (but not impossible) to overcome.

People who have experienced trauma are likely to experience high anxiety, hypervigilance and hyperarousal (being on edge and very aware, along with looking for threats in their environment), problems regulating their emotions, and more. They may also re-experience the event in the form of flashbacks and intrusive, disturbing thoughts. Someone with these symptoms will usually be diagnosed with Post-traumatic stress disorder (PTSD). You can see how some of these symptoms of PTSD overlap with those of OCD.

Trauma, particularly in childhood, can increase the chances of OCD developing. Trauma can also be the catalyst for the onset of OCD in someone who is more predisposed to the disorder. Both OCD and PTSD center around having intrusive thoughts and trying to ‘cope’ with those thoughts, often in ways that actually perpetuate the mental illness. With OCD, these are the compulsive behaviours we’ve discussed. When it comes to PTSD, patients often try to ‘cope’ with their thoughts by isolating themselves, suppressing the thoughts, turning to distractions and utilizing other unhealthy coping mechanisms.

If you’ve been through trauma in your life, it’s understandable that you would be anxious about something bad happening again. It’s easy to see how this can lead to a need to try to control your environment and prevent any potential threats, which can lead to OCD symptoms. The charity PTSD UK states that, “It’s understandable that for people who have experienced a traumatic event, they may constantly feel anxious and have concerns about their safety – the compulsive behaviors may make a person feel more in control, safe, and reduce anxiety in the short-term.”

Psychological Factors

Personality type

Some research shows that if you have certain personality traits, this can make you more likely to develop OCD. The mental health charity Mind shares an example, “if you are a neat, meticulous, methodical person with high standards, you may be more likely to develop OCD.”

Of course, the type of personality you have isn’t going to cause OCD, but it can make you more predisposed to developing the disorder. The personality traits patients of OCD have been shown to possess include:

  • A need to have things ‘perfect’ or ‘just right
  • Having a hard time making decisions
  • Being impulsive
  • A tendency to take on more responsibility than people without OCD, or a tendency to feel more responsible for themselves and others
  • A habit of avoiding situations which might be perceived as dangerous or risky
6 types of dysfunctional beliefs

We all have intrusive thoughts. It’s how we interpret those thoughts and the significance we attach to them which can lead to OCD. If we have an intrusive thought and simply let it pass us by, or think ‘that was a bit strange’ and then don’t worry about it, it doesn’t have any consequences.

However, if we have an intrusive thought and misinterpret the thought as being extremely important, threatening, having the potential to lead to something negative or thinking it makes us a bad person for example, this can lead to the need to try to ‘deal’ with the thought to lessen those feelings. If this continues over time, it can lead to OCD. The thoughts are the obsessions which can develop over time, and the actions we might try to take to cope with these obsessions become compulsions.

OCD UK explains that, “The repeated misinterpretation of intrusive thoughts leads to the development of the obsessions and because the thoughts are so distressing, the individual engages in compulsive behaviour to try to resist, block, or neutralise the obsessive thoughts.”

A group of researchers called The Obsessive-Compulsive Cognitions Working Group have identified 6 dysfunctional beliefs which they believe contribute to OCD and fuel the ongoing OCD cycle. They theorize that if an individual has these dysfunctional beliefs, they are likely to struggle with OCD.

  • Inflated responsibility

    This means you feel a sense of responsibility which is ‘increased’ or disproportionate to the situation. You may believe you have the ability to cause a negative situation (for example feeling that if you don’t carry out a compulsion something bad will happen). You may also feel you are responsible for preventing negative events (such as feeling you are responsible for the safety of your family through your compulsions).

  • Thought-action fusion

    Thought-action fusion means that you place a great deal of importance on your thoughts. You may hear this referred to as ‘over importance of thoughts’. It simply means that you think having a thought is the same as actually carrying out an action. So if you have a ‘bad’ intrusive thought, such as imagining you hurt somebody, you may think that makes you a bad person in the same way as if you actually carried out that action.

    You might also believe that thinking about a negative event actually increases the probability of it happening. For example if you think about someone having an accident, you may believe that this increases the chances of the accident occurring.

  • Control of thoughts

    As it sounds, this means that you think it’s possible to have full control of your thoughts. More than that, you may think it’s essential that you do.

  • Overestimation of threat

    This means you may be more inclined to think that negative events are likely as an outcome. You may also be more likely to think that these negative events are going to be extremely severe. You may feel more alert to threats and feel as though these threats are very dangerous.

  • Perfectionism

    You may feel that everything has to be perfect (yourself included), and that anything which is imperfect is not acceptable.

  • Intolerance for uncertainty

    You may find that you become increasingly anxious when facing the unknown. You may believe it’s vital to know definitively that a negative event is not going to happen.

Stress as a catalyst

While stress cannot be the sole cause of OCD, stressful events can serve as a catalyst to trigger the onset of OCD in someone who is predisposed to developing the disorder. Likewise, times of stress can worsen existing anxiety and OCD symptoms. These stressful events can be anything depending on the individual, including:

  • Loss of a loved one
  • A divorce (or parents getting divorced in the case of children)
  • Moving home (or school)
  • Financial difficulties
  • Job loss
Personal experience

Some theories suggest that if when you were growing up, you saw a loved one with OCD using compulsive behaviours to cope with anxiety, you may have learnt these behaviours as a coping mechanism. This is particularly likely if you observed this during your formative years. Even if a loved one didn’t have OCD but was particularly anxious, you may have picked up on certain anxiety behaviours and learnt from them.

Other theories suggest that the environment you are brought up in can also have a significant impact on how your OCD develops and even what type of OCD you may develop. The beliefs you are brought up around can influence what you perceive as ‘bad’ thoughts. This doesn’t always stem from something harmful within the environment, although it can.

For example, if you are brought up to understand that illegal drugs are wrong and can be very harmful (as many of us are), if you later have an intrusive thought about taking a drug, you may worry about this and feel it makes you a bad person. This may then develop into a compulsion. Similarly, if you grow up with a parent who puts great emphasis on cleaning (even if it isn’t a compulsion for the parent), you may be more likely to develop contamination OCD.

In the same way if you are brought up around a harmful belief, such as being brought up around someone who is homophobic, as you grow up and hopefully distance yourself from these beliefs, you may still interpret intrusive thoughts about being gay as ‘negative’ and therefore develop obsessions around them. However as more research is being done, some professionals are swaying away from these theories.

If a child is not taught appropriate ways to deal with stressful situations and to cope with worries by their parents or caregivers, they are left to try to figure this out themselves. This in itself can be stressful and as this study explains can lead the child to develop, “maladaptive coping techniques such as obsessions and compulsions as a way to manage the distress felt about situations that seem uncontrollable.”

Maintenance of OCD behaviours

If once or twice you dealt with some of your intrusive thoughts by carrying out a compulsion, and at first it reduced your anxiety a little bit (as compulsions can tend to do when they first begin), your brain makes that connection that carrying out that action is an effective way to reduce anxiety. Unfortunately, as this becomes a ‘coping’ mechanism, the compulsions grow and the anxiety actually increases over time rather than decreases. This is how OCD behaviours are often inadvertently maintained.

Comorbid Mental Illness or Neurological Conditions

It’s understood that if you have another mental illness or neurological condition, you may be more likely to develop OCD. The research is clear that often OCD and other mental illnesses (such as depression, mood disorders and other anxiety disorders) commonly go hand in hand, but whether one is more likely to come first and ‘cause’ the other is unclear. What we do know is that many symptoms of other mental illnesses overlap with that of OCD and share the same neural pathways in the brain.

Research has shown a strong correlation between OCD and Tourette’s syndrome (TS), which is a neurological disorder causing people to ‘tic’ involuntarily. These tics are movements or sounds which the patient cannot control. Both TS and OCD share some of the same neural pathways. They also share some of the same genes.This study concluded that, “The pattern of comorbidity and other evidence indicates that the TS gene(s) may be responsible for a spectrum of disorders, including OCD.” This 2019 study also concluded that there are genetic overlaps between TS and OCD.

There are also high rates of comorbidity between Autism spectrum disorders and OCD. This study explains that, “as many as 30–40% of autistic patients are also diagnosed with OCD”. Many of the repetitive behaviours shown in OCD are also shown in any autism disorders, suggesting that they may share the same pathways in the brain. Some studies which have investigated this theory found that some similar brain regions are involved in both types of disorder.

Perinatal OCD

Perinatal OCD occurs when a woman is pregnant or after she gives birth. The International OCD Foundation explains that, “the perinatal period (from pregnancy to 12 months after childbirth) is a particularly vulnerable time for symptoms of OCD to appear, whether they be entirely new symptoms or a re-occurrence of OCD after a period of remission.”

This means that even if an individual has never experienced OCD symptoms previously, pregnancy can be a trigger for OCD. The Royal College of Psychiatrists state that, “OCD affects 2 in 100 women in pregnancy and 2 -3 in every 100 women in the year after giving birth.”

The exact reason for perinatal OCD is not known, but it’s thought that the significant hormonal changes which women go through during pregnancy can also influence brain chemistry. This change in brain chemistry causes the same type of brain activity seen in patients with OCD.

Some experts believe that the rise in oxytocin in particular (a hormone which helps the mother bond with the child) can cause a high ‘protection response’. This makes mothers more likely to be hypervigilant, on the lookout for threats, and to be overly anxious about keeping their baby safe.

Some theories suggest that the increased level of responsibility that mothers experience can make them feel particularly anxious about the safety of their baby and anything which may harm them. This can increase to the point of obsession, which can then lead to OCD.

Perinatal OCD typically begins with obsessional thoughts, such fears about the safety of the baby, fear of the baby being contaminated or becoming ill, or intrusive thoughts about aggression towards the baby. Intrusive thoughts about aggression can be very distressing but don’t mean the mother is actually going to hurt the baby. As we’ve mentioned previously, we all experience intrusive thoughts and it doesn’t mean that we really feel that way, or that we’re going to act on them. In fact this is common even in parents without OCD, with the difference being that they don’t attach any significant meaning to the thoughts, as opposed to someone with OCD who experiences these thoughts as very important and stressing. This study explains that, “the experience of intrusions regarding deliberate or accidental harm occurs in 80% of the general population and even more commonly in new parents.”

These obsessions can lead to compulsions to desperately try to ‘get rid of’ these horrible thoughts. This may involve compulsively cleaning the baby or their belongings, avoiding contact with the baby, frequently checking the baby, seeking reassurance from another adult about the baby’s health and more. However as we know, unfortunately compulsions actually worsen OCD.

Perinatal OCD can lead to disturbed attachments between the mother and child, as well as being very distressing. However just like other forms of OCD, it can be effectively treated and managed to allow mother and baby to thrive together.

Traumatic Brain Injury (TBI)

A traumatic brain injury (TBI) is a severe injury to the brain which can be caused by any major accident or physical trauma. This could include road accidents, falls, or an assault for example. The National Institutes of Health explain that, “A TBI is caused by an external force that injures the brain. It can occur when a person’s head is hit, bumped, or jolted.”

Understandably this sort of severe injury to the brain can cause a lot of changes, including cognitive functioning difficulties, mobility impairment and more. The effects a TBI has depends on which areas of the brain are affected by the injury. In the case of some TBIs, the areas of the brain which contribute to obsessions and compulsions can be affected, leading to the development of OCD. OCD can develop straight after the injury, or may not be diagnosed until months later depending on each individual case.

Pediatric Acute-onset Neuropsychiatric Syndrome (PANS)

PANS is the sudden development of OCD symptoms in a child after an infection. Many infections ‘hide’ within the host (the child) by mimicking other cells within the child’s body. When the infection is discovered, the child’s immune system starts to try and fight off the infection by producing antibodies. However because of this mimicry, sometimes the child’s immune system will mistakenly attack the types of cells that were being mimicked, ‘thinking’ that it’s fighting the infection. With PANS it’s thought that the child’s immune system attacks an area of the brain during this process, leading to obsessive compulsive symptoms.

PANS used to be called Pediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcus (PANDAS) when it was thought that only a strep infection was the cause. However more recent research has shown that other infections can also have the same results.

The Immune System: Developing Research

For a number of years now ongoing research has shown that the immune system could play a vital part in causing OCD. It’s thought that the immune system in OCD patients is not functioning correctly, causing a range of problems including obsessive and compulsive symptoms. This would fit in with the cause of PANS, with the immune system attacking an area of the brain in children which then leads to OCD symptoms. This research is still developing as scientists look into this potential cause of OCD in more depth.

This year this research has developed further with a new study by a group of scientists who pinpointed increased levels of a specific protein in patients with OCD. This protein is called Immuno-moodulin (Imood), and is within the lymphocytes of the OCD patients tested. Lymphocytes are a type of immune cell, so this would fit in with the other developing theories.

Even more excitingly, the researchers working on this study have tested an antibody treatment in mice with compulsive symptoms and the same high levels of Imood, and discovered the treatment reduced the mice’s anxiety behaviours. Professor Fulvio D’Acquisto, a professor of immunology at the University of Roehampton who is leading the research, is now working with other scientists on the project to develop an antibody treatment for humans with OCD.

The treatment could take up to 5 years before it can be taken to clinical trials. Although the treatment being available for OCD patients is still a long way off, it’s highly promising! Professor Fulvio D’Acquisto states that, “It is early still, but the discovery of antibodies — instead of the classical chemical drugs — for the treatment of mental disorders could radically change the life of these patients as we foresee a reduced chance of side effects.”


Beyond OCD, (2019), “What Causes OCD?”

Stanford Medicine (2019), “Understanding Obsessive-Compulsive and Related Disorders”.

James V .Luceya, Durval C.Costa, Geraldo Busatto, et al, (1997), “Caudate regional cerebral blood flow in obsessive-compulsive disorder, panic disorder and healthy controls on single photon emission computerised tomography”. Psychiatry Research: Neuroimaging, Volume 74, Issue 1, 14 March 1997, Pages 25-33

Christian, C. J., Lencz, T., Robinson, D. G., Burdick, K. E., et al,. (2008). “Gray matter structural alterations in obsessive-compulsive disorder: relationship to neuropsychological functions.” Psychiatry research, 164(2), 123–131.

Ilse Graat, Martijn Figee, Damiaan Denys, (2017), “Neurotransmitter Dysregulation in OCD”. Obsessive-compulsive Disorder: Phenomenology, Pathophysiology, and Treatment, Oxford Medicine Online.

Caleb W Lack, (2015), “The etiology of Obsessive-Compulsive Disorder”. Obsessive-Compulsive Disorder: Etiology, Phenomenology, and Treatment (pp.25-42) Edition: 1st, Onus Books

The National Institute of Mental Health Information Resource Center, (2020), “Obsessive-Compulsive Disorder”. National Institutes of Health (NIH).

Owen Kelly, PhD, (2019), “Is Obsessive Compulsive Disorder Genetic?”. Very Well Mind.

The Center for Treatment of Anxiety and Mood Disorders, (2017), “What is Trauma?”.

PTSD UK, (2020), “OCD and PTSD – and the relationship between the two”.

Min Jung Huh, Geumsook Shim, Min Soo Byun, (2013), “The Impact of Personality Traits on Ratings of Obsessive-Compulsive Symptoms”. Psychiatry Investigation 2013;10(3):259-265

Mind, (2020), “What causes OCD?”.

Owen Kelly, PhD, (2020), “Personality Traits That May Make OCD More Likely”. Very Well Mind.

OCD UK, (2020), “What causes OCD”.

Dykshoorn K. L. (2014). “Trauma-related obsessive-compulsive disorder: a review.” Health psychology and behavioral medicine, 2(1), 517–528.

Dianne M.Sheppard, John L.Bradshaw, Rosemary Purcell, Christos Pantelis, (1999), “Tourette’s and comorbid syndromes: Obsessive compulsive and attention deficit hyperactivity disorder. a common etiology?”. Clinical Psychology Review, Volume 19, Issue 5, August 1999, Pages 531-552

Joanna Widomska, Janita Bralten, Marijn Martens, et al, (2019), “M70 – DETERMINING THE GENETIC OVERLAP BETWEEN TOURETTE SYNDROME (TS), OBSESSIVE COMPULSIVE DISORDER (OCD) AND OCD/TIC-RELATED TRAITS”. European Neuropsychopharmacology

Volume 29, Supplement 3, 2019, Pages S992-S993

Ting, J. T., & Feng, G. (2011). “Neurobiology of obsessive-compulsive disorder: insights into neural circuitry dysfunction through mouse genetics”. Current opinion in neurobiology, 21(6), 842–848.

Carlisi, C. O., Norman, L., Murphy, C. M., Christakou, A., et al,. (2017). “Disorder-Specific and Shared Brain Abnormalities During Vigilance in Autism and Obsessive-Compulsive Disorder.” Biological psychiatry. Cognitive neuroscience and neuroimaging, 2(8), 644–654.

Neha Hudepohl, MD, Margaret Howard, PhD, (2014), “Perinatal OCD: What Research Says About Diagnosis and Treatment”. International OCD Foundation.

Royal College of Psychiatrists, (2018), “Perinatal OCD”.

Challacombe, F. L., & Wroe, A. L. (2013). “A hidden problem: consequences of the misdiagnosis of perinatal obsessive-compulsive disorder.” The British journal of general practice : the journal of the Royal College of General Practitioners, 63(610), 275–276.

National Institute of Child Health and Human Development, (2016), “What causes TBI?”. National Institutes of Health.

Marco A. Grados, (2003), “Obsessive-compulsive disorder after traumatic brain injury”. International Review of Psychiatry, Issue 4, Volume 15, pgs 350-358, Johns Hopkins University.

Leonardo F Fontenelle, Izabela Guimarães Barbosa, Juliano Victor Luna, (2012), “A cytokine study of adult patients with obsessive-compulsive disorder”. Comprehensive Psychiatry, Volume 53, Issue 6, August 2012, Pages 797-804

Donatella Marazziti, Federico Mucci, Leonardo F.Fontenelle, (2018), “Immune system and obsessive-compulsive disorder”. Psychoneuroendocrinology, Volume 93, July 2018, Pages 39-44

Queen Mary University of London. (2020), “Antibodies could provide new treatment for OCD.” ScienceDaily. ScienceDaily, 21 April 2020.

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Ann-Marie D'Arcy-Sharpe

Ann-Marie D'Arcy-Sharpe has been working as a freelance writer for 7+ years, primarily in the health and wellness niche. Her passion is writing about mental health, chronic illness, and general wellness (including self-love, confidence, happiness, and self-improvement).

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